A hybrid transmission for a vehicle typically includes a plurality of clutches and a pair of electric motors for delivering mechanical power to a drive system of the vehicle. To operate properly, the transmission usually requires a supply of pressurized fluid, such as conventional transmission oil. The pressurized fluid may be used for such functions as cooling, lubrication, and, in some cases, operation of the torque transfer devices. The lubricating and cooling capabilities of transmission oil systems impact the reliability and durability of the transmission. Additionally, multi-speed transmissions require pressurized fluid for controlled engagement and disengagement of the torque transmitting mechanisms that operate to establish the speed ratios within the internal gear arrangement.
Typically, pressurized fluid flows from a pump through valves and passages in a first electro-hydraulic circuit to the clutches for operating the clutches. From within the transmission, the fluid drains into a sump in the transmission where it is reused. The electric motors in the hybrid transmission can transform electric power into mechanical power for operating the drive system. During operation of the transmission, the electric motors generate heat and cooling of the electric motors is required. To cool the motors, a second electro-hydraulic circuit is used to move fluid to cool the electric motors.